An Example of Negative Ageing

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Mike Fontenot

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May 14, 2021, 12:54:07 PM5/14/21
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In what follows, I refer to the perpetually-inertial twin as "she", and
to the twin who instantaneously changes his velocity as "he".

I've worked out an example that shows an instantaneous negative ageing
for her, according to him, when CMIF (co-moving inertial frame)
simultaneity is used ...i.e., she instantaneously gets YOUNGER according
to him, when using the CMIF simultaneity method. And I'll show the
results for this example for my simultaneity method, which gives no
discontinuities and gives no negative ageing.

First, here's a description of the Minkowski diagram (with time tau on
the horizontal axis and separation X on the vertical axis). That always
has to be determined first.

The two "twins" in this case aren't really twins ... they are just
babies who were born at the same time but 20 lightyears (ly) apart, and
with zero relative velocity. This situation continues until they are
both 40 years old. We represent this initial situation by drawing a
horizontal line on the diagram at the point X = 20 on the vertical axis,
extending from tau = 0 to tau = 40. That is the initial segment of his
worldline. At the end of that first segment, write 40 immediately above
the end of that segment of his worldline to show his age , and
vertically below there write 40 immediately below the horizontal axis to
show her age.

Then, he instantaneously changes their relative velocity to v = 0.57735
ly/y, and continues that velocity for the rest of their lives. This
causes his worldline to slope upward toward the right at a slope of
0.57735 (and an angle wrt the horizontal axis of 30 degrees). Label that
point where the second segment of his worldline starts as point T.

Next, draw a 45 degree line starting at the point 40 on the horizontal
axis, and sloping upward to the right, representing the worldline of a
light pulse that she transmits when she is 40, and that is moving toward
him. We then write an equation giving X as a function of tau for that
light pulse, and then we write another equation giving X as a function
of tau for the upward sloping segment of his worldline. Then, we set
those two equations equal (force their X values to be equal). The result
gives the value of tau where those two lines intersect ... label that
point Q. That point is vertically above the point tau = 87.32 on the
horizontal axis. Write that value just below the horizontal axis,
vertically below that point of intersection.

We also need to determine their separation according to her (the value
of X) when she is 87.32. The answer is 47.32 ly.

Next, we need to plot two lines of simultaneity (LOS's) that show what
"Now" is for him. (The LOS's for her are just vertical lines). His LOS's
(anywhere for him when his velocity is 0.57735) have slope 1/v =
1/o.57735 = 1.73, and they make an angle of 60 degrees wrt the
horizontal axis. The first LOS we need goes through point Q. That line
intersects the horizontal axis at the point tau = 60. That is determined
by writing the X(tau) equation for that LOS, and solving it when X is
set to zero. So this tells us that when he is 78.63 years old, she is
60, according to him.

Next, we need to determine how old she says he is when she is 60. We
know that according to her, he ages slower than she does by the factor
gamma = 1.2247 (once he has changed his velocity to 0.57735). So
according to her, while she ages from 40 to 60, he ages from 40 to
56.33. Mark that age on his worldline.

We also need to determine their separation according to her (the value
of X) when she is 60. The answer is 31.55 ly.

Next, we do the same thing for the LOS that goes through the point T
where his worldline starts sloping upward. The result is that her age
when he changes velocity is 28.45, according to him. He was 40 then.

From the above information, we can draw the Age Correspondence Diagram
(the ACD), which is a plot of her age (on the vertical axis), according
to him, versus his age (on the horizontal axis).

During the first segment, their relative velocity is zero, so they each
agree that they are ageing at the same rate. Therefore the first segment
of the ACD is just a line of slope 1, sloping upward to the right,
making a 45 degree angle wrt the horizontal axis. This first segment is
the same, regardless of whether you are using the CMIF simultaneity
method, or my method. Label the end of that segment point T.

In the CMIF method, at point T, when he changes velocity from zero to
0.57735, he says that she instantaneously gets younger by 11.55 years,
from 40 to 28.45. So, for the CMIF case, we draw a vertical line
downward from point T, of length 11.55 ly. Then, the next (last) segment
slopes upward forever at a slope of 1/gamma = 0.8165.

What does the plot look like after the point T in the case of my
simultaneity method? It is a straight line between the point T and the
point Q. Point Q is where his age is 78.64 and her age is 60. It is a
point on the third segment of the CMIF line we determined above. Point Q
is where he received the pulse from her, and it is the end of the
"Disagreement Interval" (DI) between him and the a perpetually-inertial
observer who is co-located and co-moving with him. So, after point Q,
the ACD for my method coincides with the CMIF method for the rest of
their lives. I.e., after the end of the disagreement interval (DI), the
CMIF method and my method agree thereafter in this example.

So, as was claimed, with my method, the ACD has no discontinuities, and
no negative ageing (i.e., the ACD plot never slopes downward).

I personally prefer the CMIF method, because of its simplicity, and
because I'm not bothered by discontinuities or by negative ageing. But
for those people who ARE bothered by those characteristics of the CMIF
method (and in my experience, that's a LOT of people), my method offers
a safe refuge.

Dono.

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May 14, 2021, 12:59:40 PM5/14/21
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On Friday, May 14, 2021 at 9:54:07 AM UTC-7, Mike_Fontenot wrote:
> snip fresh cretinisms<

Proper time can only be positive.

mitchr...@gmail.com

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May 14, 2021, 1:41:44 PM5/14/21
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Positivity is the reality of quantity in math.
There is no zero time rate or end of time....
There is no negative aging just forward slow time that cannot end.
The atom can't be pushed to the speed limit.
BH doesn't exist because of Gamma limiting gravity push
below the speed limit. Just as a space ship cannot
heat push its autodynamic propulsion to reach
light speed...

Mitchell Raemsch

Michael Moroney

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May 14, 2021, 2:34:35 PM5/14/21
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On 5/14/2021 12:54 PM, Mike Fontenot wrote:
>
> The two "twins" in this case aren't really twins ... they are just
> babies who were born at the same time but 20 lightyears (ly) apart, and
> with zero relative velocity.

Same time in which frame? Person A will be 20 years old when she
receives news that Person B was born, and Person B will be 20 years old
when he receives news that Person A was born.

Thomas 'PointedEars' Lahn

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May 14, 2021, 3:17:31 PM5/14/21
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Mike Fontenot wrote:

> So, as was claimed, with my method, the ACD has no discontinuities, and
> no negative ageing (i.e., the ACD plot never slopes downward).

Since *nobody* except *you* claimed that “negative ageing” would occur
in standard special relativity, this result is unsurprising. You have
just successfully beaten your own straw man. Congratulations.

*facepalm*


PointedEars
--
Q: Who's on the case when the electricity goes out?
A: Sherlock Ohms.

(from: WolframAlpha)

mitchr...@gmail.com

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May 14, 2021, 8:02:57 PM5/14/21
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On Friday, May 14, 2021 at 9:54:07 AM UTC-7, Mike_Fontenot wrote:
> In what follows, I refer to the perpetually-inertial twin as "she", and
> to the twin who instantaneously changes his velocity as "he".

You can't keep any atomic motion inertial because of gravity being
an influence changing it... if the twin is in gravity it is accelerating
or decelerating...

Tom Roberts

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May 15, 2021, 11:35:32 AM5/15/21
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On 5/14/21 11:54 AM, Mike Fontenot wrote:
> I've worked out an example that shows an instantaneous negative ageing
> for her, according to him, [...]

Which means that your notion of "ageing" is completely different from
what everybody else considers it to be. Your meaning is useless.

Tom Roberts

Mike Fontenot

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May 15, 2021, 12:59:35 PM5/15/21
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The famous physicist Brian Greene disagrees with you:

Skip to the 23:14 point on this link:

https://www.pbs.org/wgbh/nova/video/the-fabric-of-the-cosmos-the-illusion-of-time/

mitchr...@gmail.com

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May 15, 2021, 7:58:32 PM5/15/21
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On Saturday, May 15, 2021 at 9:59:35 AM UTC-7, Mike_Fontenot wrote:
> On 5/15/21 9:35 AM, Tom Roberts wrote:
> > On 5/14/21 11:54 AM, Mike Fontenot wrote:
> >> I've worked out an example that shows an instantaneous negative ageing
> >> for her, according to him, [...]
> >
> > Which means that your notion of "ageing" is completely different from
> > what everybody else considers it to be. Your meaning is useless.
> >
> > Tom Roberts
> The famous physicist Brian Greene disagrees with you:
>

Mike? Brian Greene is a fake. He had to beat Einstein about OCR
and Einstein has won in history. They tested OCR by
the 2 slit experiment without observers. And Bohr
lost. His science was just fiction and Einstein was
right all along...

Mitchell Raemsch

Cliff Hallston

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May 15, 2021, 10:58:50 PM5/15/21
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On Saturday, May 15, 2021 at 9:59:35 AM UTC-7, Mike_Fontenot wrote:
> > ...your notion of "ageing" is completely different from what everybody else
> > considers it to be...
> >
> The famous physicist Brian Greene disagrees with you...

That video doesn't refer to "negative aging", it just talks about the usual relativity of simultaneity (which it incorrectly conflates with time dilation) of relatively moving systems of coordinates, and notes that the alien's time slice (temporal foliation) tilts in different directions in time depending on the direction of motion of the alien. This does not mean the distant person's age is jumping around as the alien changes directions on his bicycle.

Overall, you seem to be missing some important facts when you type various mappings between separate world lines. For example, a distant person can directly receive information about your location and proper time for all past times up to the event at which you intersect with his past light cone. That's the last event of yours from which the distant observer can have received any information about your whereabouts and clock reading. Anything beyond that is just extrapolation on his part. Soon after that event a grizzly bear could jump out of the bushes and chase you to a separate location (or even tear you limb from limb), and the distant person cannot know about this. So he can only extrapolate. What should he assume for your extrapolated trajectory as you advance beyond his past light cone?

The simplest assumption would be that you continue your trajectory from that last reported event, when your clock read tau1, all the way until you reach his future light cone, and he can easily calculate the value tau2 that your clock reads at that event. Then it would be quite natural for him to map his current moment to you on that extrapolated world line when your clock reads (tau1+tau2)/2. You could do the same for him, computing the value of his proper time that you choose to map to your current time, based on extrapolating his trajectory from the last report on your past light cone to your future light cone.

Needless to say, even if your extrapolations turn out to be exactly correct, these mappings are not reflexive, meaning that if he maps his event p to your event q, you would generally not map your event q to his event p. However, lack of reflexivity doesn't seem to bother you. Another limitation is that the extrapolations may not be exactly correct, and might not even be approximately correct. If the other person accelerates significantly after he sends the last message that has reached you, your assessment of his time and place later will obviously be wrong, and there is nothing you can possibly do about this, since superluminal signaling is not possible. Granted, you could agree in advance that he's going to accelerate in a specific profile, but it's still an extrapolation.

You could also say that you aren't trying to define the mapping in real time, you are willing to wait until the world lines have been established in the past, and simply establish the mappings for those. In that case you would just use (tau1+tau2)/2 with the actual value of tau2. Then the only problem is that it's not reflexive. There's nothing you can do about that.

Ironically this mapping depends on the trajectory of the distant object, not on the trajectory of the person trying to establish a mapping (contrary to the slices of the co-moving inertial coordinate systems). But, as always, these are just specific mappings of which there are infinitely many. In Greene's dumbed-down cartoon he is just referring to simple inertial mapping, and trying to make it sound as weird and wacky as possible, rather than giving a grown-up explanation of the relativity of simultaneity and incomplete ordering induced by the Minkowski metric. It isn't a good idea to try to learn special relativity from videos like that.

mitchr...@gmail.com

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May 15, 2021, 11:17:53 PM5/15/21
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Negative aging would begin in the future...

Mitchell Raemsch

Sylvia Else

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May 16, 2021, 12:03:24 AM5/16/21
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On 15-May-21 2:54 am, Mike Fontenot wrote:
>
> I've worked out an example that shows an instantaneous negative ageing
> for her, according to him, when CMIF (co-moving inertial frame)
> simultaneity is used ...i.e., she instantaneously gets YOUNGER according
> to him, when using the CMIF simultaneity method. And I'll show the
> results for this example for my simultaneity method, which gives no
> discontinuities and gives no negative ageing.

You're talking about something, her age, which is not measurable by him,
when he's not colocated with her. It's a mathematical artefact, arising
from applying a theoretical model to an inappropriate situation, and
nothing more than that.

Sylvia.

JanPB

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May 16, 2021, 12:07:31 AM5/16/21
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On Friday, May 14, 2021 at 9:54:07 AM UTC-7, Mike_Fontenot wrote:
> In what follows, I refer to the perpetually-inertial twin as "she", and
> to the twin who instantaneously changes his velocity as "he".

Bottom line is in relativity there is no such thing as simultaneity at a distance.

Any mention of it within the theory refers to a *defined* notion, typically
designed to mimic the intuitive "everyday" human experience (and
Newtonian physics). And such defined notions are not even necessarily
unique.

It has no physical meaning otherwise. It's a man-made accounting system only.

--
Jan

Maciej Wozniak

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May 16, 2021, 12:43:30 AM5/16/21
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On Sunday, 16 May 2021 at 06:07:31 UTC+2, JanPB wrote:
> On Friday, May 14, 2021 at 9:54:07 AM UTC-7, Mike_Fontenot wrote:
> > In what follows, I refer to the perpetually-inertial twin as "she", and
> > to the twin who instantaneously changes his velocity as "he".
> Bottom line is in relativity there is no such thing as simultaneity at a distance.

Sure, your Shit was unable to create the basic functionality of
a model of space; of course it doesn't change that it's far
BETTER than anything else.

Thomas 'PointedEars' Lahn

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May 16, 2021, 9:11:01 AM5/16/21
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“We're sorry, but this video is not available.”


PointedEars
--
Q: How many theoretical physicists specializing in general relativity
does it take to change a light bulb?
A: Two: one to hold the bulb and one to rotate the universe.
(from: WolframAlpha)

Thomas 'PointedEars' Lahn

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May 16, 2021, 10:23:39 AM5/16/21
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Thomas 'PointedEars' Lahn wrote:

> Mike Fontenot wrote:
>> On 5/15/21 9:35 AM, Tom Roberts wrote:
>>> On 5/14/21 11:54 AM, Mike Fontenot wrote:
>>>> I've worked out an example that shows an instantaneous negative ageing
>>>> for her, according to him, [...]
>>>
>>> Which means that your notion of "ageing" is completely different from
>>> what everybody else considers it to be. Your meaning is useless.
>>>
>>> Tom Roberts
>>
>> The famous physicist Brian Greene disagrees with you:
>>
>> Skip to the 23:14 point on this link:
>>
>> https://www.pbs.org/wgbh/nova/video/the-fabric-of-the-cosmos-the-illusion-of-time/
>
> “We're sorry, but this video is not available.”

(JFTR)

Apparently this video is only available from the USA. I managed to
watch it by using the free Hola! VPN Chrome extension in Chromium:

<https://hola.org/products>

Probably other VPN products would work as well:

<https://thebestvpndeals.com/best-vpn/safe-vpn/>


PointedEars
--
Q: What did the female magnet say to the male magnet?
A: From the back, I found you repulsive, but from the front
I find myself very attracted to you.
(from: WolframAlpha)

Mike Fontenot

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May 16, 2021, 10:24:10 AM5/16/21
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On 5/15/21 10:07 PM, JanPB wrote:
>
> Bottom line is in relativity there is no such thing as simultaneity at a distance.
>

Do you think that the distant person ceases to exist when they are
separated?

It seems to me that, if the distant person EXISTS at that instant in the
life of the accelerating observer, she must be DOING SOMETHING at that
instant, and her brain must be in some UNIQUE STATE at that instant.
And for each unique state of her brain, there is a unique instant in her
life. Therefore she must have a specific age according to him, at that
instant in his life. It follows that the only way she doesn't have a
specific age, according to him, at that instant in his life, is if she
DOESN'T EXIST at that instant, according to him.

Cliff Hallston

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May 16, 2021, 12:43:36 PM5/16/21
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On Sunday, May 16, 2021 at 7:24:10 AM UTC-7, Mike_Fontenot wrote:
> On 5/15/21 10:07 PM, JanPB wrote:
> > Bottom line is in relativity there is no such thing as simultaneity at a distance.
> >
> Do you think that the distant person ceases to exist when they are
> separated?

When people say silly things like "there is no such thing as simultaneity at a distance" you just have to ignore them. The correct statement is that "simultaneous" means "at the same value of the time coordinate", and there are infinitely many different temporal foliations, even if we restrict ourselves to just the space-like foliations that respect causality. So the problem with your reasoning is not that "there is no such thing as simultaneity" (which is like saying there is no such thing as velocity), it's that simultaneity is coordinate-dependent, and hence not unique. Of course, operationally defined coordinate systems have physical meaning, but there are infinitely many of them.

> It seems to me that, if the distant person EXISTS at that instant in the
> life of the accelerating observer...

Look closely at what you typed there. Please note that the phrase "in the life of the accelerating observer" refers to the world line of that person, and an "instant" in that life is an event on that world line. By definition, a distant object (i.e., an object that is not at that event) does not exist at that event. Of course, an object exists at other events, but there are infinitely many space-like ways of mapping the events along one world line with the events along another world line, all of which lie between the causal past and the causal future of each other. Also, as explained in my previous post, any such mappings are necessarily conjectural extrapolations from the most recent information we could have received from the distant object on our past light cone.

Mike Fontenot

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May 16, 2021, 1:41:09 PM5/16/21
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On 5/15/21 10:03 PM, Sylvia Else wrote:
>
> You're talking about something, her age, which is not measurable by him,
> when he's not colocated with her. It's a mathematical artefact, arising
> from applying a theoretical model to an inappropriate situation, and
> nothing more than that.
>

I don't seen any "inappropriate" situation.

And simultaneity at a distance IS measurable by each and every
perpetually-inertial observer (PIO) ... Einstein showed us clearly how
to do that. But there appears to be no way that an accelerated observer
can measure it, PURELY ON HIS OWN.

But, given the assumption that the CMIF simultaneity method makes (that
the accelerated observer must, at each instant of his life, always agree
with the perpetually-inertial observer (the PIO) who is co-located and
mutually stationary with him at that instant), he CAN measured her age,
because his PIO can measure her age.

And given the assumption that MY simultaneity method makes (that he must
agree with what the PIO in the left half of the Minkowski diagram says
about how much she aged during the portion of the light pulse that is in
the left half plane, and likewise for the PIO in the right-half plane),
he CAN measure her age.

But it IS very troubling to me that there doesn't seem to be any way to
determine, by measurement, what her current age is, according to the
accelerated observer, without making any assumption at all. I.e.,
without specifying a simultaneity method, he can't measure her current
age. That means there is apparently no way to determine which
simultaneity method is correct.

Sylvia Else

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May 17, 2021, 7:13:17 AM5/17/21
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On 17-May-21 3:41 am, Mike Fontenot wrote:
> On 5/15/21 10:03 PM, Sylvia Else wrote:
>>
>> You're talking about something, her age, which is not measurable by
>> him, when he's not colocated with her. It's a mathematical artefact,
>> arising from applying a theoretical model to an inappropriate
>> situation, and nothing more than that.
>>
>
> I don't seen any "inappropriate" situation.
>
> And simultaneity at a distance IS measurable by each and every
> perpetually-inertial observer (PIO) ... Einstein showed us clearly how
> to do that.

He provided a theoretical framework which allows the correct calculation
of things that can be measured. That is not the same as saying how to
measure things.

With your example, when he plugs in his current time, and her distance
from him, as calculated by him, the theory gives him a time, but it is
not her time, it is the time he need's to plug into a theory about the
propagation of light in order to determine what he'll see if he points a
telescope at her. The measurement he makes is of her apparent age as
represented by the light as it arrives at his location.

The arriving light can be measured. All the rest is just numbers and
formulae.

Sylvia.

Jeff-Relf.Me

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May 17, 2021, 8:17:34 AM5/17/21
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Is she a baby ?... 95 years old ?
Mostly, you can tell her age just by looking at her.
No need for general- or special- relativity.

Mike Fontenot

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May 17, 2021, 10:21:50 AM5/17/21
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On 5/17/21 5:13 AM, Sylvia Else wrote:
> [...]
> With your example, when he plugs in his current time, and her distance
> from him, as calculated by him, the theory gives him a time, but it is
> not her time, it is the time he need's to plug into a theory about the
> propagation of light in order to determine what he'll see if he points a
> telescope at her. The measurement he makes is of her apparent age as
> represented by the light as it arrives at his location.
>

The image he sees of her (which she transmitted as a TV signal) is
certainly not a current picture of her. It shows what she looked like a
long time ago, when she transmitted the image. So that doesn't tell him
what her current age is at all.

A perpetually-inertial observer (PIO) could also see an OLD image of
her. But he could also use the time dilation equation (or the Lorentz
equations) to determine her CURRENT age at any instant in his life.
There's no doubt that a PIO can determine the current age of a distant
person. The question is, if that current age is a meaningful concept
for the PIO, why isn't it a meaningful concept for an accelerated observer?

Tom Roberts

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May 17, 2021, 11:00:27 AM5/17/21
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On 5/15/21 11:07 PM, JanPB wrote:
> Bottom line is in relativity there is no such thing as simultaneity at a distance.

That's just plain wrong. But simultaneity at a distance is not a
physical phenomenon, it is rather a defined relationship determined by a
human convention, and there are infinitely many of them available to
choose from.

> It's a man-made accounting system only.

Yes. So clearly it is not "no such thing". But also, no physical
phenomena can be affected by such a man-made accounting system, only
DESCRIPTIONS of phenomena are affected.

Tom Roberts

Maciej Wozniak

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May 17, 2021, 11:42:30 AM5/17/21
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On Monday, 17 May 2021 at 17:00:27 UTC+2, tjrob137 wrote:
> On 5/15/21 11:07 PM, JanPB wrote:
> > Bottom line is in relativity there is no such thing as simultaneity at a distance.
> That's just plain wrong. But simultaneity at a distance is not a
> physical phenomenon, it is rather a defined relationship determined by a
> human convention, and

And your tales of zillions of experiments confirming your
CONVENTION is a pure, nonsensical lie.


> Yes. So clearly it is not "no such thing". But also, no physical
> phenomena can be affected by such a man-made accounting system

An idiot says!!!!! An idiot is an incredibly wise guru!!!!
Must be true.
Don't we, humans, affect some physical phenomena,
idiot?

Mike Fontenot

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May 17, 2021, 1:02:29 PM5/17/21
to
On 5/17/21 9:00 AM, Tom Roberts wrote:
>
> [...] But simultaneity at a distance is not a
> physical phenomenon, it is rather a defined relationship determined by a
> human convention, and there are infinitely many of them available to
> choose from.
>

There are an infinite number of them, because there are an infinite
number of potential observers who might want to know "how old is she
right now?". But for each such observer, at each instant of his life,
there is only ONE correct answer.

For perpetually-inertial observers, it is clear how that one correct
answer is obtained: via the time dilation equation, or via the Lorentz
equations.

But for an observer who sometimes accelerates, that one correct answer
isn't known, because we don't know which of the known simultaneity
methods is correct. (For each of the four methods, the answer can be
determined, though.) And since it seems to be impossible to determine
the correct answer experimentally, we can't determine which of the known
simultaneity methods is correct (if any).

mitchr...@gmail.com

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May 17, 2021, 2:22:35 PM5/17/21
to
There is no negative aging. But there is different aging.
Time can slow by gravity and motion... but nothing
can end it. Everything shares the beginning common BB age.
Even as space in between has expanded.


Mitchell Raemsch

Cliff Hallston

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May 17, 2021, 2:29:15 PM5/17/21
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On Monday, May 17, 2021 at 10:02:29 AM UTC-7, Mike_Fontenot wrote:
> There are an infinite number of potential observers who might want to
> know "how old is she right now?". But for each such observer, at each
> instant of his life, there is only ONE correct answer.

But there are infinitely many different definitions of "correct", corresponding to infinitely many different mappings between the events on two separate world lines. So your reasoning is specious.

Also, the most recent information you can have about a distant object is from your past light cone, so you cannot possibly know if a spacelike-separated object is in the location you extrapolated, or even if that object has exploded. It might not even exist on any of the (infinitely many) temporal foliations that include your event. This shows that you cannot possibly "know" at event p on your world line the reading on a clock at a spacelike-separated event q.

> For perpetually-inertial observers, it is clear how that one correct
> answer is obtained: via the time dilation equation, or via the Lorentz
> equations.

No, that's garbled. The correct statement would be that any given system of inertial coordinates entails a temporal foliation for the time coordinate that defines one particular mapping between the events of spatially separate world lines. But there are infinitely many different inertial coordinate systems, with different temporal foliations, so that mapping is not unique. You must not conflate an object or observer with a coordinate system. If an object is at rest in terms of such a coordinate system, we may or may not decide to describe events in terms of that system, but it is incorrect to conflate any object with a coordinate system. And even if we restrict ourselves to unaccelerated coordinate systems in which we are at rest, there are still infinitely many such systems with different temporal foliations. And of course if we consider accelerating systems the range of different systems is still greater. Lastly, inertial coordinate systems are not "obtained" by a "time dilation equation", nor even by what you call "Lorentz equations", they are defined intrinsically.

> But for an observer who sometimes accelerates, that one correct answer
> isn't known, because we don't know which of the known simultaneity
> methods is correct.

That's wrong, because you are still conflating observers with coordinate systems, and you still have not defined "correct", and it isn't that the "correct" answer isn't known, it's that there are infinitely many different definitions of "correct".

> For each of the four methods, the answer can be determined, though.

There are not just four possible mappings, there are infinitely many.

> And since it seems to be impossible to determine the correct answer experimentally...

We can determine the correct answer, but only after the word "correct" has been defined. Your first task is to define what *you* mean by "the correct mapping", and you must define this in a non-circular way. You can't just say the correct mapping is the mapping that is correct. And once you define correctness, it will be pointed out (again) that there are infinitely many possible definitions of correctness, so you won't have made any progress.

> we can't determine which of the known simultaneity methods is correct (if any).

Again, all your statements about correctness are meaningless unless and until you give a meaningful definition of "the correct mapping between the events on spatially separate world lines". If you can't define it, then you obviously can't determine it. Also, when providing your definition, please keep in mind that you can't even know where a distant object is, or whether it has exploded, subsequent to when it exited the past light cone of your present instant. If you're willing to extrapolate, then the optimal answer is easy (see earlier post), and if youre not willing to extrapolate, then the answer is completely indeterminate.

Mike Fontenot

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May 17, 2021, 3:21:20 PM5/17/21
to
On 5/17/21 12:22 PM, mitchr...@gmail.com wrote:
> There is no negative aging.

Cliff Hallston

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May 17, 2021, 3:33:24 PM5/17/21
to
On Monday, May 17, 2021 at 12:21:20 PM UTC-7, Mike_Fontenot wrote:
> > There is no negative aging.
>
> The famous physicist Brian Greene disagrees with you:
> Skip to the 23:14 point on this link:
> https://www.pbs.org/wgbh/nova/video/the-fabric-of-the-cosmos-the-illusion-of-time/

The video does not talk about negative aging. You might have simply been making an honest mistake when you made that false claim the first time, but since the falsity was pointed out, and you now repeat the claim, I don't think your behavior can be called anything other than lying.

Here's the quote from the previous post, correcting your mis-statement: "That video doesn't refer to "negative aging", it just talks about the usual relativity of simultaneity (which it incorrectly conflates with time dilation) for relatively moving systems of inertial coordinates, and notes that the time slice (temporal foliation) of the inertial coordinates in which the alien is at rest tilts in different directions in time depending on the direction of motion of the alien. This does not mean the distant person's age is jumping around as the alien changes directions on his bicycle."

If there's something about this explanation that you disagree with or don't understand, then go ahead and express it.

Mike Fontenot

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May 17, 2021, 3:40:48 PM5/17/21
to
On 5/17/21 1:33 PM, Cliff Hallston wrote:
> On Monday, May 17, 2021 at 12:21:20 PM UTC-7, Mike_Fontenot wrote:
>>> There is no negative aging.
>>
>> The famous physicist Brian Greene disagrees with you:
>> Skip to the 23:14 point on this link:
>> https://www.pbs.org/wgbh/nova/video/the-fabric-of-the-cosmos-the-illusion-of-time/
>
> The video does not talk about negative aging.

In the video, Brian Greene says that when the alien starts riding his
bike in the direction AWAY from the earth, he concludes that time on
earth goes backward by 200 years. THAT is negative ageing.

Odd Bodkin

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May 17, 2021, 4:07:48 PM5/17/21
to
No, Mike, that’s not what Brian said. What he said is that when he starts
riding his bike, the events that are coincident with “now” for the alien
correspond to a different set of events than when the alien was stopped.
There is no implication of negative aging. It simply means that the pairs
of events that are deemed simultaneous between the earth and the alien
planet are different, depending on whether the bike is moving or not.

Here’s a simple example to explain. Suppose you are a blind man and you are
listening to the radio, and you’re aware of the thunderstorm outside.
Suddenly your radio goes out, in the middle of a report from the station
about a mile away. Five seconds later, you hear thunder. You ask yourself,
was that lightning strike perhaps responsible for the radio going out?
Well, the speed of sound is about a mile per five seconds, and since you
heard the thunder five seconds later, you can clock that time delay
backwards and conclude that, yes, the lightning responsible for the
thunderclap probably took out the radio station. The lightning strike and
the radio going out were, for practical purposes, simultaneous, though you
did not hear the signal from the lightning strike until five seconds later.


What relativity adds to this is that, even after accounting for propagation
delays, if you are moving relative to the radio station, then the thing
that happened a mile away did not happen five seconds before but longer
before.

--
Odd Bodkin -- maker of fine toys, tools, tables

Cliff Hallston

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May 17, 2021, 4:35:44 PM5/17/21
to
On Monday, May 17, 2021 at 12:40:48 PM UTC-7, Mike_Fontenot wrote:
> > The video does not talk about negative aging.
>
> In the video, Brian Greene says that when the alien starts riding his
> bike in the direction AWAY from the earth, he concludes that time on
> earth goes backward by 200 years. THAT is negative ageing.

Nope, he says "The alien's 'now' slice has swept back through more than 200 years of earth history". This does not say or imply that anything "ages negatively", nor that the man by the gas station becomes unborn and retroactively ceases to exist, etc. It is talking (in a dumb cartoonish way) about the extrapolated temporal slices of systems of inertial coordinates.

Note also that it is misleading to talk about the "now slice sweeping", because inertial "now slices" do not sweep. What he is really talking about is a sequence of inertial coordinate systems, and taking a slice of constant t from each one, but this sequence of slices does not constitute an inertial coordinate system, and hence the skews between those slices don't represent a sweeping of an inertial "now slice". So admittedly it's a poor and misleading exposition, but even so, it does not make the mistake of claiming "negative aging". The concept of negative aging is just your silly misconception.

Thomas 'PointedEars' Lahn

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May 17, 2021, 4:44:20 PM5/17/21
to
Mike Fontenot wrote:

> On 5/15/21 9:35 AM, Tom Roberts wrote:
>> On 5/14/21 11:54 AM, Mike Fontenot wrote:
>>> I've worked out an example that shows an instantaneous negative ageing
>>> for her, according to him, [...]
>>
>> Which means that your notion of "ageing" is completely different from
>> what everybody else considers it to be. Your meaning is useless.
>
> The famous physicist Brian Greene disagrees with you:
>
> Skip to the 23:14 point on this link:
>
> https://www.pbs.org/wgbh/nova/video/the-fabric-of-the-cosmos-the-illusion-of-time/

First of all, note that what Brian Greene is stating there is the typical
*popular*-scientific version of special relativity: “Since motion slows the
passage of time, their clocks will no longer tick off time at the same
rate.”

As has been explained (here/by me) many times before, that is NOT what
happens. Instead, a different *amount* of proper time *elapses* in the
different reference frames. It only *appears* as if time would be passing
slower in the moving frame when clocks at rest in different frames are
*compared*.

However, what he says about the “now-slice of the alien” is basically
correct (although it has nothing to do with “time dilation”; it is a
related, but different effect called “the relativity of simultaneity”).

But the rest is your *misinterpretation* of what he is saying as, instead of
correcting your misconceptions about relativity, you are trying to fit what
he is correctly saying into the framework of your misconceptions:

At *no* time (no pun intended) does he say that one of the participants in
that experiment considers or observes the other to be aging differently,
in particular he does NOT say that the “person on Earth” is "aging
negatively".

And if you think about it more deeply, it is quite ridiculous to assume that
the biological processes of a lifeform 10 billion light-years away could be
affected by some arbitrary motion of the other, that is even only a motion
when a suitable reference frame is chosen. Instead, it is *purely* a
*geometrical* effect.


PointedEars
--
Q: Where are offenders sentenced for light crimes?
A: To a prism.

(from: WolframAlpha)

Thomas 'PointedEars' Lahn

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May 17, 2021, 4:47:20 PM5/17/21
to
if a suitable reference frame is chosen. Instead, it is *purely* a

Sylvia Else

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May 17, 2021, 7:34:56 PM5/17/21
to
It's not even meaningful for the PIO. Two momentarily colocated PIOs
seeing the same light would get different results for her current age.

Sylvia.

Mike Fontenot

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May 17, 2021, 8:16:51 PM5/17/21
to
Yes they would. But the current age they each get for her is completely
meaningful for each of them.

If this weren't true, there would be no need for the Lorentz equations,
or for the famous time dilation equation (TDE).

Einstein spent a lot of time developing both of those equations, and a
lot of time explaining how an array of perpetually-inertial observers,
who are mutually stationary and holding synchronized clocks, can
determine the current time of moving clocks (or equivalently, the
current ages of moving distant persons).

Sylvia Else

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May 17, 2021, 10:20:47 PM5/17/21
to
On 18-May-21 10:16 am, Mike Fontenot wrote:
> On 5/17/21 5:34 PM, Sylvia Else wrote:
>> On 18-May-21 12:21 am, Mike Fontenot wrote:
>>>
>>> A perpetually-inertial observer (PIO) could also see an OLD image of
>>> her.  But he could also use the time dilation equation (or the
>>> Lorentz equations) to determine her CURRENT age at any instant in his
>>> life. There's no doubt that a PIO can determine the current age of a
>>> distant person.  The question is, if that current age is a meaningful
>>> concept for the PIO, why isn't it a meaningful concept for an
>>> accelerated observer?
>>
>> It's not even meaningful for the PIO. Two momentarily colocated PIOs
>> seeing the same light would get different results for her current age.
>>
>
> Yes they would.  But the current age they each get for her is completely
> meaningful for each of them.
>
> If this weren't true, there would be no need for the Lorentz equations,
> or for the famous time dilation equation (TDE).

Special Relativity is part of the model we use to describe reality. It
replaced the part of that model which previously assumed that times and
distances were absolute. Attempting to use special relativity on its own
produces numbers that are meaningless.

Sylvia.

Cliff Hallston

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May 17, 2021, 10:32:00 PM5/17/21
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On Monday, May 17, 2021 at 5:16:51 PM UTC-7, Mike_Fontenot wrote:
> The current age they each get for her is completely meaningful for each of them.

You continue to conflate objects (or observers) with coordinate systems, and you continue to mistakenly think that because something is meaningful it is therefore unique. And you continue to mistakenly think that a sequence of time slices from a sequence of different systems of inertial coordinates inherit the meanings that those slices have in the context of their respective systems. (They do not.)

> If this weren't true, there would be no need for the Lorentz equations,
> or for the famous time dilation equation (TDE).

You completely misunderstand, on several levels. First, the content of special relativity is local Lorentz invariance, which signifies that the equations of physics take the very same simple homogeneous and isotropic form in terms of any system of inertial coordinates, and those systems are related by Lorentz transformations. What you comically refer to as "the famous time dilation equation" is just a partial derivative of the time component of the Lorentz transformation. This simple relates the time coordinates along a specific world line for two relatively moving systems of inertial coordinates. It does not have magical or mystical significance beyond that.

> Einstein spent a lot of time developing both of those equations, and a
> lot of time explaining how an array of perpetually-inertial observers,
> who are mutually stationary and holding synchronized clocks, can
> determine the current time of moving clocks...

Einstein elucidated the relations between relatively moving systems of inertial coordinates. He was not silly enough to refer to "perpetually inertial observers", which is a phrase that conflates objects with coordinate systems. That is not a mistake that Einstein ever made.

Again, the last information you can have about the position and time of a distant object comes from your past light cone, so there is no unique mapping to a later event based on the information available to you at any given time. It can only be based on extrapolation, and once you understand this, the simplest extrapolation is obvious, leading to the mapping (tau1+tau2)/2 explained previously. Naturally this is not a reflexive relation, as explained previously.

Jeff-Relf.Me

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May 18, 2021, 1:07:26 AM5/18/21
to
Mike Fontenot:
> There are an infinite number of potential observers
> who might want to know "how old is she right now?".

Only if you replace "an infinite number of" with "zero".

Earth to Mike Fontenot... Earth to Mike Fontenot...
no one (honestly) cares, not even you.

Thomas 'PointedEars' Lahn

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May 18, 2021, 9:03:23 AM5/18/21
to
Mike Fontenot wrote:

> Einstein spent a lot of time […] explaining how an array of perpetually-
> inertial observers, who are mutually stationary and holding synchronized
> clocks, can determine the current time of moving clocks (or equivalently,
> the current ages of moving distant persons).

Actually, he did not. That is merely your fantasy.


PointedEars
--
«Nec fasces, nec opes, sola artis sceptra perennant.»
(“Neither high office nor power, only the scepters of science survive.”)

—Tycho Brahe, astronomer (1546-1601): inscription at Hven

Tom Roberts

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May 18, 2021, 12:33:28 PM5/18/21
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On 5/16/21 9:24 AM, Mike Fontenot wrote:
> It seems to me that, if the distant person EXISTS at that instant in
> the life of the accelerating observer, she must be DOING SOMETHING at
> that instant, and her brain must be in some UNIQUE STATE at that
> instant. [... further nonsense ignored]

You are completely ignoring the actual issue:

Which instant along the distant person's worldline corresponds
to a given instant along the accelerating observer's worldline?

During the period of interest these worldlines are spacelike separated,
so there is no unique and compelling answer to this question, all you
can do is pontificate about which method you think is best.

As the distant person is essentially at rest in an inertial frame, IMHO
the most reasonable approach is to use that frame to define distant
simultaneity. So the accelerating observer continually keeps track of
their current position and time relative to that frame. Note they would
surely do this independent of any desire to know the "current age of the
distant person", because they must navigate among objects essentially at
rest in that frame.

Tom Roberts

Tom Roberts

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May 18, 2021, 12:38:16 PM5/18/21
to
On 5/17/21 12:02 PM, Mike Fontenot wrote:
> On 5/17/21 9:00 AM, Tom Roberts wrote:
>> [...] But simultaneity at a distance is not a physical phenomenon, it
>> is rather a defined relationship determined by a human convention, and
>> there are infinitely many of them available to choose from.
>
> There are an infinite number of them, because there are an infinite
> number of potential observers who might want to know "how old is she
> right now?".  But for each such observer, at each instant of his life,
> there is only ONE correct answer.

Your attempt to impose your personal hopes and dreams on nature is
doomed. The world we inhabit is just not like that -- there are many
correct numbers, because a HUMAN defines what is "correct", and many
such definitions are possible.

> For perpetually-inertial observers, it is clear how that one correct
> answer is obtained: via the time dilation equation, or via the Lorentz
> equations.

Hmmm. There's still the ambiguity of which inertial frame to use: that
of the observer or that of the distant person?

Tom Roberts

Ace Hubner

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May 18, 2021, 1:09:02 PM5/18/21
to
Thomas 'PointedEars' Lahn wrote:

> First of all, note that what Brian Greene is stating there is the
> typical *popular*-scientific version of special relativity: “Since
> motion slows the passage of time, their clocks will no longer tick off
> time at the same rate.”
> As has been explained (here/by me) many times before, that is NOT what
> happens. Instead, a different *amount* of proper time *elapses* in the
> different reference frames. It only *appears* as if time would be
> passing slower in the moving frame when clocks at rest in different
> frames are *compared*.

idiot, you contradict yourself. Chose one and stay with it. I would
guess, all the times you explain (here/by you) before, is nothing more
than *incoherent_idiocy*.

Mike Fontenot

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May 18, 2021, 1:30:23 PM5/18/21
to
On 5/18/21 10:33 AM, Tom Roberts wrote:
>
> You are completely ignoring the actual issue:
>
>     Which instant along the distant person's worldline corresponds
>     to a given instant along the accelerating observer's worldline?
>

It depends on who's asking the question. For each questioner, there is
a single correct answer. If the questioner is a perpetually-inertial
observer, they can determine that correct answer. But if the questioner
sometimes accelerates, to get an answer they have to chose one method
from among the two known simultaneity methods that obey the principle of
causality (CMIF or mine), and use it to determine the answer. And there
seems to be no way to determine which of those two methods is correct
(if either). The accelerated observer can't choose to use the answer
given by the distant home twin, because she says the traveling twin is
aging more slowly than she is, and he knows that just the opposite is
true on the outbound leg.

Mike Fontenot

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May 18, 2021, 1:45:14 PM5/18/21
to
On 5/18/21 10:38 AM, Tom Roberts wrote:
>
> Your attempt to impose your personal hopes and dreams on nature is
> doomed. The world we inhabit is just not like that -- there are many
> correct numbers, because a HUMAN defines what is "correct", and many
> such definitions are possible.
>

I disagree. I don't believe that the distant person (she) ceases to
exist whenever she is distant from me. And if she exists, her brain is
in a definite state right then. That brain state defines a definite age
for her right then.

__________________


(I said: "For perpetually-inertial observers, it is clear how that one
correct answer is obtained: via the time dilation equation, or via the
Lorentz equations.")
>
> Hmmm. There's still the ambiguity of which inertial frame to use: that
> of the observer or that of the distant person?
>

There's no ambiguity, and no choice to be made: use the frame of the
perpetually-inertial person who is asking the question!

mitchr...@gmail.com

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May 18, 2021, 2:04:41 PM5/18/21
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You would have to stop time first before it could go to aging backward.
But nothing can stop time... not gravity and not propulsion.
There is a gravity limit on acceleration as well...
It is Gamma below light speed for the atom.
The atom does not go to rest or to light speed...
That is not in the Gamma for it.

Mitchell Raemsch

Cliff Hallston

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May 18, 2021, 2:26:16 PM5/18/21
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On Tuesday, May 18, 2021 at 10:30:23 AM UTC-7, Mike_Fontenot wrote:
> It depends on who's asking the question. For each questioner, there is
> a single correct answer.

No, you've been shown multiple distinct "answers", and which of them is "correct" depends entirely on what definition of "correct" you choose. Each of those answers is "correct" according to itself. Each of them respects causality. Each of them is based on extrapolating the world line of the distant object.

> If the questioner is a perpetually-inertial observer, they can determine that correct answer.

Anyone, in any state of motion, can determine infinitely many different mappings between the events along two separate world lines. You've been shown explicitly many different ways of doing this, all of which are "correct" according to themselves. Yes, inertial coordinate systems have distinguished properties, but this does not imply that there is a unique mapping. Also, you are still conflating objects with coordinate systems.

> the two known simultaneity methods that obey the principle of causality (CMIF or mine)...

No, there are infinitely many temporal foliations that obey the principle of causality.

Again, allowing for accelerations of both world lines, it is necessary to extrapolate from the past light cone, at which the distant object's proper time is known to be tau_past, to the future light cone, at which by it past spatial position and trajectory with the simplest linear extrapolation we know the proper time of the distant object as tau_future. Then we map our current event with the event on the distant world line with proper time (tau_past + tau_future)/2. Of course, like all such trajectory-dependent methods, this is not reflexive or transitive. Understand?

Ace Hubner

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May 18, 2021, 2:27:22 PM5/18/21
to
Mike Fontenot wrote:

> On 5/18/21 10:38 AM, Tom Roberts wrote:
>>
>> Your attempt to impose your personal hopes and dreams on nature is
>> doomed. The world we inhabit is just not like that -- there are many
>> correct numbers, because a HUMAN defines what is "correct", and many
>> such definitions are possible.
>
> I disagree. I don't believe that the distant person (she) ceases to
> exist whenever she is distant from me. And if she exists, her brain is
> in a definite state right then. That brain state defines a definite age
> for her right then.

*slow_now* is not about aging. "You are entirely and completely
incorrect".

Ace Hubner

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May 18, 2021, 2:31:45 PM5/18/21
to
We don't talk with germans.

Tom Roberts

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May 18, 2021, 4:42:38 PM5/18/21
to
On 5/18/21 12:30 PM, Mike Fontenot wrote:
> On 5/18/21 10:33 AM, Tom Roberts wrote:
>>
>> You are completely ignoring the actual issue:
>>
>>      Which instant along the distant person's worldline corresponds
>>      to a given instant along the accelerating observer's worldline?
>>
>
> It depends on who's asking the question.  For each questioner, there is
> a single correct answer.

This is just plain not true -- there are many possible definitions of
"correct". You are trying to impose your personal hopes and dreams onto
the world. That's ridiculous!

But there's no point in repeating what has already been said many times.

Tom Roberts

mitchr...@gmail.com

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May 18, 2021, 5:44:05 PM5/18/21
to
The future is waiting to come back through time...
Where is a tachyon getting its negative time and energy?
Isn't Higgs for particle energy? How negative from the
future?

Mitchell Raemsch

Mike Fontenot

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May 18, 2021, 6:41:57 PM5/18/21
to
On 5/18/21 2:42 PM, Tom Roberts wrote:
>
> This is just plain not true -- there are many possible definitions of
> "correct".

Let's get specific. Take the simple case where there are two
perpetually-inertial observers (PIO's): she and he, moving apart at a
relative speed v = 0.866 ly/yr. And suppose that in the past, when they
were momentarily co-located, they were each zero years old.

Then consider the question you asked: "How old is she when he is 40?"

Let's say you asked her that question when she is 100. Her answer would
be "When he was 40, I was 80." She gets that answer in a very easy and
foolproof way: she knows from the time dilation equation (TDE) that he
always ages at half the rate that she does (because for v = 0.866, gamma
= 2.0). Or, equivalently, she says she always ages twice as fast as he
does. There's no wiggle room there ... there is no other correct answer
for her ... no other definition of "correct".

Now, ask him the same question: "How old was she when you were 40?". He
uses the TDE to correctly conclude that "she was 20 when I was 40".
There's no wiggle room there either ... there is no other correct answer
for him ... no other definition of "correct".

Those two perpetually-inertial observers give different answers to the
same question. Neither can correctly give any answer other than the
answer they gave, And they are both right.


Cliff Hallston

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May 18, 2021, 8:59:08 PM5/18/21
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On Tuesday, May 18, 2021 at 3:41:57 PM UTC-7, Mike_Fontenot wrote:
> Take the simple case where there are two [twins] moving apart at a
> relative speed v = 0.866 ly/yr. In the past, when they were momentarily
> co-located, they were each zero years old. [Each one says] "When he was
> 40, I was 80." There is no other correct answer ...

You keep missing the point. All you are doing is noting for any object moving at speed v in terms of an inertial coordinate system x,t the rate of proper time is dtau/dt = sqrt(1-v^2/c^2). Your are saying that each twin uses the simultaneity of the inertial coordinate system in terms of which that twin is at rest. But that is not the only possible definition of "correct". In fact, Einstein himself gave an alternative example early in his 1905 paper, and he emphasized the freedom in the choice of simultaneity. He clearly acknowledged the obvious fact that the convention of using inertial synchronization is not the only possible one, but merely that it is (in many circumstances) a very *practical* one (his word).

In general, there are infinitely many different ways in which we can map the events of one world line to the events of another, even if we restrict ourselves to the foliations of inertial coordinate systems. I will give you three examples.

First, everyone on and near the earth might use the ECI coordinates, which has a single global temporal foliation. With this system, people in moving cars and satellites in orbit and planes flying over head all use the same global time coordinate, regardless of their relative speeds (so they have to correct for Sagnac, etc). The proper time of each world line is then simply the integrated elapsed time along that world line, and this gives a definite correct answer to all questions about comparing the proper times simultaneously, meaning at the same value of the global time coordinate. This has the great advantage that the simultaneity relations are all reflexive and transitive. This is a perfectly correct system.

For a second example, space travelers who undergo accelerations to relativistic speeds could very well use the cosmological coordinate system in which the CMBR and the light from distant galaxies are maximally isotropic. All the stars and galaxies and planets are moving at fairly low speeds in terms of this global coordinate system, so this gives a very good and useful global mapping, and the simultaneity is reflexive and transitive. This is a perfectly correct system.

For a third example, without invoking any third entities, suppose someone at event e1 wants to know the proper time on a distant clock "simultaneous" with e1. Well, the most recent information from the distant clock gives its position and proper time tau_past on the past light cone of e1. Since we are allowing for acceleration, we don't know for sure how the distant clock moves after tau_past, so we can only extrapolate, and the simplest extrapolation is linear, based on which we can compute tau_future where the distant clock's trajectory reaches the future light cone of e1. Now, to respect causality, someone at e1 knows that the "current" time on the distant clock must be between tau_past and tau_future, and one perfectly reasonable convention is to say it is the average of those, i.e., (tau_past + tau_future)/2. This is a perfectly good convention, and you may notice that in your twins example it gives the opposite results, i.e., in that example each twin effectively uses the foliation of the inertial coordinates in which the *other* twin is at rest. This is not reflexive or transitive, but it is a perfectly "correct" method.

There are infinitely many other perfectly "correct" methods. This is all well known, and was thoroughly discussed in the early days of relativity - see the conventionality of simultaneity.

Mike Fontenot

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May 19, 2021, 10:05:28 AM5/19/21
to
On 5/18/21 6:59 PM, Cliff Hallston wrote:
> On Tuesday, May 18, 2021 at 3:41:57 PM UTC-7, Mike_Fontenot wrote:
>>
>> [Each one says] "When he was
>> 40, I was 80."

You misquoted me (in those square brackets) in the above sentence. What
I actually said was:

"Her answer would be 'When he was 40, I was 80.' "

Cliff Hallston

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May 19, 2021, 11:23:02 AM5/19/21
to
On Wednesday, May 19, 2021 at 7:05:28 AM UTC-7, Mike_Fontenot wrote:
> >> [Each one says] "When he was 40, I was 80."
>
> What I actually said was...

So you deny that your claim is that each one says that when they are 80 their twin is 40?

Remember, you are saying that each twin uses the mapping given by the inertial coordinates in which that twin is at rest. According to those mappings, the event of each twin at 80 maps to the event of the other twin at 40. Do you deny that this is your claim?

Mike Fontenot

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May 19, 2021, 12:29:38 PM5/19/21
to
On 5/19/21 9:23 AM, Cliff Hallston wrote:
>
> So you deny that your claim is that each one says that when they are 80 their twin is 40?
>

She says that when he was 40, she was 80.

He says that when he was 40, she was 20.

Message has been deleted

Cliff Hallston

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May 19, 2021, 5:34:08 PM5/19/21
to
On Wednesday, May 19, 2021 at 9:29:38 AM UTC-7, Mike_Fontenot wrote:
> > So you deny that your claim is that each one says that when they are 80 their twin is 40?
> >
> She says that when he was 40, she was 80.
> He says that when he was 40, she was 20.

That doesnt contradict what I said. Again, do you agree that, in terms of the inertial coordinates in which either twin is at rest, when that twin is 80 the other twin is 40?

Since that is just Relativity 101, I assume you agree, and the point is that those two mappings are just two of infinitely many inertial foliations, in addition to the infinitely many more non-inertial foliations. A few examples were given in the previous message. Each of these has its own physical meaning, but none of them are uniquely "correct". They are all equally "correct".

Mike Fontenot

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May 19, 2021, 6:43:45 PM5/19/21
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On 5/19/21 3:34 PM, Cliff Hallston wrote:
>
> Since that is just Relativity 101, I assume you agree, and the point is that those two mappings are just two of infinitely many inertial foliations, in addition to the infinitely many more non-inertial foliations. A few examples were given in the previous message. Each of these has its own physical meaning, but none of them are uniquely "correct". They are all equally "correct".
>

For a given perpetually-inertial observer (the "home twin", her), there
is only one answer to the question, "How old is that distant person
right now?", that agrees with her own measurements. The way she can
make those measurements was described in detail by Einstein: a
collection of equally-spaced clocks are laid out that are stationary
with respect to her, and they are all synchronized via light signals.
There is a perpetually-inertial observer at each clock. Those observers
keep a record of every person who goes flying past them, recording the
time on that person's clock, and what their own clock shows at that
instant. They are then (long after the fact) able to communicate that
information to the home twin. That tells her that when she was aged 80,
the traveler (he) was aged 40. And SURPRISE! That result is exactly
what the time dilation equation (the TDE) told her, long ago. The TDE
told her that result immediately, without the long delay that the
measurements took. ANY other answer will disagree with what the
measurements say. There is only one correct answer.

Cliff Hallston

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May 19, 2021, 7:49:19 PM5/19/21
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On Wednesday, May 19, 2021 at 3:43:45 PM UTC-7, Mike_Fontenot wrote:
> For a given perpetually-inertial observer (the "home twin", her), there
> is only one answer to the question, "How old is that distant person
> right now?", that agrees with her own measurements.

Correction: In terms of any given system of inertia-based coordinates x,y,z,t (defined so that the equations of physics take their simple homogeneous and isotropic form) there is a unique simultaneity, i.e., two events are simultaneous in terms of this coordinate system if and only if they occur at the same value of t. This applies to the inertial coordinates in which you are at rest, but it also applies to any other system of inertial coordinates.

> The way she can make those measurements was described in detail by Einstein....

Einstein described how to establish a system of inertia based coordinates in any given frame, i.e., a system of coordinates in which (as he said) the equations of Newtonian mechanics hold good (in the low speed limit). There are infinitely many such systems, each with its own temporal foliation. That's why there is no unique simultaneity between distant events, as Einstein explained. Note that he also gave an example of a different kind of coordinate system (one of infinitely many), and he stressed the freedom we have in choose the most convenient simultaneity convention for whatever coordinate system we choose.

> There is a perpetually-inertial observer at each clock.

No, this is the core of your misconception. You need to recognize that coordinate systems are not observers, and observers are not coordinate systems. Anyone can use any system of coordinates they like. In fact, we often use coordinate systems in terms of which we are not at rest. Your confusion isn't entirely your fault, because many popular expositions of relativity use the word "observer" as shorthand for a system of inertial coordinates, and this misleads many students into an erroneous identification of observers with coordinate systems in which they are at rest.

> There is only one correct answer.

Correction: There is only one correct answer about simultaneity for any given system of coordinates, namely, two events are simultaneous if they occur at equal t values. But simultaneity is not unique, because there are infinitely many different systems of coordinates, each with their own temporal foliations, and there is no uniquely "correct" association of observers with coordinate systems.

Any observers can make and express measurements in terms of any system of coordinates they like. For example, astronomers typically make measurements of the solar system in terms of sun-centered coordinates, even though we (on earth) are not at rest in terms of those coordinates. The simultaneity of Sun-centered coordinates is different than the simultaneity of earth centered coordinates, which is different than the simultaneity of your car centered coordinates, and so on, and these are all different than the simultaneity of coordinates in which the CMBR is isotropic. We can and do make measurements in terms of all of these (regardless of our own state of motion), so simultaneity between distant events is not unique.

mitchr...@gmail.com

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May 20, 2021, 3:07:29 PM5/20/21
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Negative aging is like negative parallax.
Parallax has to go infinite in distance first but that cannot
be done in the closed finite universe...
You can only slow time not end it.
If you can't end it first you cannot
create a negative rate for anything...

Mitchell Raemsch

Mike Fontenot

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May 23, 2021, 10:39:13 AM5/23/21
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On 5/18/21 10:38 AM, Tom Roberts wrote:
>
> Hmmm. There's still the ambiguity of which inertial frame to use: that
> of the observer or that of the distant person?
>

Suppose the "home twin" (she) and the "traveling twin" (he) are both
perpetually inertial, and have a relative speed of 0.866 ly/yr, so that
gamma = 2.0.

She can set up HER co-stationary grid of synchronized clocks, along with
a "helper observer" stationed at each of those clocks. He can also set
up HIS co-stationary grid of synchronized clocks, together with a
"helper observer" stationed at each clock. They each synchronize their
own grid of clocks by sending light signals between their clocks, and
make use of the fact that they know what the speed of light is, and that
it is constant.

He can eventually determine what her current age was when he was age t1,
by receiving a message from his helper observer who passed her when that
helper was aged t1. That message says that she was tau1 = t1 / 2 when
she and his helper were momentarily co-located.

When he receives that message, he completely believes it, because he
knows his grid of clocks are properly synchronized. And he also has
been able to confirm (by information from his helpers) that her grid of
clocks AREN'T synchronized.

Long ago, when he was age t1, he used the time dilation equation (TDE)
to tell him that she was ageing half as fast as he was (because their
relative speed v is 0.866 ly/yr, and so gamma = 2.0). So the TDE told
him THEN, when he was age t1, that she was age t1 / 2. And now, much
later, he has been able to confirm, by the message the receives from his
helper, that the answer he got from the TDE was indeed correct.

If instead (as you prefer), he uses the inertial reference frame in
which SHE is at rest to determine how old she is when he is t1 years
old, that result will disagree with what his own system of synchronized
clocks and helpers eventually tell him. If he is a physicist, he won't
be a very successful physicist if he disregards his own measurements.



Cliff Hallston

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May 23, 2021, 2:22:26 PM5/23/21
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On Sunday, May 23, 2021 at 7:39:13 AM UTC-7, Mike_Fontenot wrote:
> If instead ... he uses [a different] inertial reference frame ... that result
> will disagree with what his own system of synchronized clocks and helpers
> eventually tell him.

You're still missing the point, and you're making two of your faulty assumptions: First, you are assuming that "correct" simultaneity is that of an inertial coordinate system in which you are at rest. Second, you are assuming that there is a unique simultaneity for coordinate systems in which you are at rest. Both of those assumptions are wrong, and this makes your belief in unique "correct" simultaneity for you doubly wrong. Let's take your erroneous assumptions one at a time:

Regarding your belief that coordinates in which we are at rest are the only correct coordinates, remember that one of the main reasons for having coordinate systems is to coordinate actions and operations for entities in a variety of states of motion. For example, if you and your friend agree to run some separate errands and then meet at the grocery story at 10:00am, you are not talking about your individual elapsed proper times, and you are not talking about an inertial coordinate system in which either of you is at rest (you will be in different states of motion in the interim), you are talking about a common temporal foliation that you both use, that is measured and established by a perfectly good system for ECI (or UTC time), based on inertial coordinates in which the Earth's center (for example) is at rest. Likewise in observations of the solar system we no longer (since Copernicus) exclusively use earth-centered coordinate systems. So you are mistaken in your belief that coordinate systems in which we are at rest are the only "correct" ones.

Now let's consider your erroneous assumption that, if we use a coordinate system in which we are at rest, there is a unique simultaneity. That's wrong too, because, as Einstein himself emphasized, we are free to synchronize clocks (at rest in a given frame) in different ways. Yes, there is physical significance in the inertial synchronization method, since it makes the equations of physics homogeneous and isotropic when expressed in terms of those coordinates, but this does not mean that these are the only "correct" synchronization. There are other synchronizations that also have physical significance. In practice we often use non-inertial coordinate systems, and of course we must then account for the effects such as centrifugal and Coriolis accelerations.

Again, within the requirements of causality, the light cone structure provides the partitioning between causal past and causal future, and there is no unique foliation in between past and future that can be called the uniquely "correct" one. Also, you cannot have any definite information about a distant object subsequent to when it exits your past light cone, so everything beyond that is necessarily extrapolated and hence indefinite.

JanPB

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May 23, 2021, 3:34:02 PM5/23/21